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Legionella – What I need To Know

The risk of human exposure to legionella at your facility is greatest when the water in your cooling tower is untreated or under-treated.  The health, environmental, and economic risks associated with a legionella outbreak at your facility is real, and is why legionella prevention should be taken very seriously.


What is legionella?

Legionellosis is the medical term for a potentially fatal, acute respiratory infection caused by any species of the gram negative, aerobic bacteria belonging to the genus Legionella. Legionella bacteria are pervasive and normally live in water and soil.  They occur organically in low numbers in natural aquatic environments.  Rivers, streams, lakes, ground water and soil are places where legionella is commonly found.  In these low numbers, legionella is basically considered harmless, however given the right environment (warmer water, the presence of micro-organisms, foulants and other nutrients) the bacteria will grow and multiply to high levels increasing the risk of exposure. The bacteria tend to grow in biofilms (slime) that are often a result of stagnant or low flow water areas. When legionella is found in high concentrations where people are, there could be trouble.  There are three broad areas that water treatment specialists look at to see if legionella could be a potential problem:

l  Does the legionella bacterium exist in any one of the various water systems in your facility?  Do any of the systems test positive for legionella?

l  Is it thriving?  Does it exceed X amount of colony forming units (cfu)?  Is the ongoing water treatment program poorly administered, poorly designed or nonexistent?

l  Can potentially infected water be aerosolized?


If the answer to any of these questions is “yes,” we look for ways to address it immediately.


Legionella in Cooling Towers

Legionella outbreaks have been linked to hot tubs, cooling towers, decorative fountains and potable water used for drinking and showering.  Hot spots for legionella include any place where untreated (or under-treated) water is warm and where it is possible for it to become aerosolized or misted.  Legionella bacteria grow best between temperatures of 72°F and 113°F (22°C – 45°C) with optimum growth temperature being 95°F and 104°F (35°C – 40°C).  High temperatures are often used to kill legionella. Cooling towers are of particular concern because they contain pools of warm water that are open to the atmosphere and present perfect breeding grounds for Legionella bacteria if they are not properly cleaned, disinfected and maintained.  Furthermore, cooling towers operate by diffusing heat and evaporated water out the top of the tower in the form of a fine mist, which may contain Legionella and other microorganisms brought in by circulating air or water.  It is for this reason that cooling towers should never be installed next to air intakes or windows that may be opened.  Major warning signs that a cooling tower is not properly treated with water treatment chemicals are if algae or scale are present in the tower.


 If you have an issue with Legionella in your cooling tower, please do not hesitate to contact us.